[PORT FROM R2] PM: add statistics debugfs file for suspend to ram.

[PORT FROM R2] PM: add statistics debugfs file for suspend to ram.

BZ: 6275

Record S3 failure time about each reason and the latest two failed
devices' name in S3 progress.
We can check it through 'suspend_stats' entry in debugfs.

Change-Id: I080c7ffe3a5539d6e0882b927438db7456d4973d
Orig-Change-Id: Ieed7fd74e27d3b482675a20cb0bb26b9054a1624
Signed-off-by: ShuoX Liu <shuox.liu@intel.com>
Signed-off-by: Loic Martin <loicx.martin@intel.com>
Reviewed-on: http://android.intel.com:8080/32873
Reviewed-by: Mansoor, Illyas <illyas.mansoor@intel.com>
Reviewed-by: Yang, Fei <fei.yang@intel.com>
Reviewed-by: buildbot <buildbot@intel.com>
Tested-by: buildbot <buildbot@intel.com>